An inside look at new Hetch Hetchy water tunnel

On this 24th anniversary of the Loma Prieta earthquake, we got a look inside a major Bay Area water project designed to survive the worst predictions for future earthquakes.

The San Francisco Public Utilities Commission is in the midst of an epic $4.6 billion water system upgrade. Sixty-two of 81 projects are completed and on Thursday we went to check out just one of those projects that is still a work in progress.

An elevator carries people 125 feet down to the mouth of the new bay tunnel. The 50-foot diameter shaft is where a boring machine has begun excavating five miles across the bay to Newark. Building the tunnel that will be the lifeline water supply from Hetch Hetchy to the Bay Area, designed to withstand the worst earthquakes predicted for the Hayward and San Andreas faults.

"One of the major projects on our water improvement program to really make our water system resilient is this bay tunnel, it is the first tunnel that is actually under the bay," said Harlan Kelly, Jr., the SFPUC general manager.

The new tunnel will replace the pipes, dating from the 1920s and 30s, which stay along the surface and go under water but never underground. In the 1990s, a PUC study showed they wouldn't survive the next big one.

"A major earthquake on one of the active faults in the Bay Area could create a catastrophic failure of the Hetch Hetchy system which in turn could result in parts of our service area to be without water for up to two months," said Julie Labonte, the bay tunnel project director.

The new tunnel is 90 percent complete and should be done by summer 2014 at a cost of $215 million or less. So far the work is six months ahead of schedule and $24 million under budget.

"Originally we had planned on making progress in the order of 50-feet a day or so. We ended up averaging 100-feet a day and on some of the good days we excavated as much as 200 feet," said Labonte.

The tunnel is made of an outer concrete ring, and an inner steel pipe that will be lined with a cement mortar.

Eventually the tunnel will connect to pipes in this shaft and then onto the peninsula.